Sodium amalgam monitor

ABSTRACT

An apparatus and method are disclosed for automatically monitoring the sodium concentration of a sodium amalgam by means of a wet chemical analysis in which a mineral acid is reacted with a sample of the sodium amalgam to generate an amount of hydrogen gas proportional to the amount of sodium in the amalgam sampled. The amount of such hydrogen gas produced is detected and displayed in units of sodium concentration. A thermal conductivity detector is preferred as the means for determining the amount of hydrogen gas produced.

This is a division, of application Ser. No. 044,295, filed May 31, 1979,now U.S. Pat. No. 4,294,798 issued on Oct. 13, 1981.

This disclosure relates to an amalgam concentration detector method andapparatus and particularly to a detector for automatically monitoringthe amount of alkali metal dissolved in the amalgam.

Sodium amalgam (NaHg) is a key intermediate in several importantcommercial processes. For example, much caustic soda technology is basedon the reaction of sodium amalgam and water; similarly, sodium methylateis manufactured from sodium amalgam and methanol, and sodiumhydrosulfite is produced by reduction of sulfur dioxide with sodiumamalgam.

Industrially, sodium amalgam is produced electrolytically and theamalgam stream piped to processes requiring it as a reactant. Theconcentrations of other reactants are scaled to sodium concentrationsobtainable in practice. Sodium levels are checked intermittently andconcentration adjustments made accordingly.

The current method for checking sodium concentration in sodium amalgamis to take a sample of the amalgam source to be measured, transport thesample to a laboratory and run a wet chemistry sodium quantitativeanalysis on the sample. The current wet chemistry quantitative analysisis to react a given quantity of the sodium amalgam with a given quantityof hydrochloric acid to generate sodium chloride and hydrogen accordingto the following reaction formula:

    NaHg+HCl→NaCl+Hg°+H.sub.2 ↑

and then measuring the volume of hydrogen gas evolved. However, themanual analysis is time-consuming and there is a need for a way of morerapidly measuring alkali metal concentrations in amalgam.

Another method proposed is that of U.S. Pat. No. 3,480,520 issued Nov.25, 1969 to R. E. Smith in which the electrical potential between analkali metal amalgam having a known concentration of alkali metal in themercury is compared to the potential of an amalgam having an unknownconcentration of alkali metal in the mercury. The amalgams of known andunknown concentrations are separated by a cation exchange membrane tohelp prevent cross-contamination. However, this reference-electrode-typeapproach has been found to be susceptible to temperature changes, torequire continual recalibration after short intervals and to be highlysusceptible to inaccuracies resulting from any leaks in or damage to themembrane within the detector. Thus, the reference electrode method hasnot proven to be of sufficient commercial reliability and there is stilla need for a rapid, alkali metal-in-amalgam detector of greaterreliability.

This need is satisfied by the method of the present invention whichprovides a method of monitoring the sodium concentration in asodium-mercury amalgam process stream, which comprises the steps of:

(a) automatically withdrawing a sample of said amalgam from said stream;

(b) automatically supplying said withdrawn sample to a reaction zone;

(c) automatically supplying a mineral acid solution to said reactionzone so as to react with said sample to generate hydrogen gas;

(d) automatically generating a signal proportional to the amount ofhydrogen gas generated per unit amount of withdrawn sample; and

(e) displaying said signal in units of sodium concentration in saidamalgam stream.

This need is also satisfied by the apparatus of the present inventionwhich provides:

(a) a reaction chamber;

(b) sample supply means, fluidly connecting said reaction chamber withsaid sodium amalgam for automatically supplying a selected sample ofsaid sodium amalgam to said reaction chamber;

(c) mineral acid supply means, for automatically supplying a sufficientquantity of mineral acid to said reaction chamber to completely reactwith and remove any sodium from said amalgam and producing a quantity ofhydrogen gas proportional to the amount of sodium in said amalgam;

(d) a liquid-gas separator in fluid communication with said reactionchamber for separating liquid and gaseous reaction products produced bysaid reaction of said mineral acid with said sodium amalgam;

(e) inert gas supply means, in selective communication with saidreaction chamber, for automatically forcing said gaseous reactionproducts out of said reaction chamber and into said liquid-gasseparator;

(f) detector means for determining the amount of hydrogen in the gasfraction from said liquid-gas separator and producing a signal which isindicative of said amount of hydrogen;

(g) a programmer for controlling the order of operation of said samplesupply means, mineral acid supply means and inert gas supply means; and

(h) display means for visually indicating the amount of said hydrogen interms of percent sodium in said sodium-mercury amalgam.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages of the invention will be better understood by referenceto the drawings, especially when taken in conjunction with the followingdetailed disclosure of the invention wherein:

FIG. 1 is a schematic drawing of the preferred amalgam monitor of theinvention for rapid, intermittent measurement;

FIG. 2 is a schematic illustration of the reactor combined with theseparator to produce an integral reactor-separator; and

FIG. 3 is a schematic illustration of the amalgam monitor using aliquid-acid solution.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 is a schematic diagram of a preferred alkali metal in amalgammonitor 10. Monitor 10 comprises a sampler 12, a reactor 14, a watersupplier 16, acid supplier 18, an inert gas supplier 20, a liquid gasseparator 22, a thermoconductivity detector 24, a programmer 26, arecorder 28 and a cleansing circuit 29, all electrically or fluidlyconnected as described below.

Sampler 12 comprises a fixed volume glass sample chamber 30, an amalgaminlet line 32, an amalgam outlet line 34, a first solenoid valve 36, asecond solenoid valve 38 and a sample outlet line 40. Inlet 32 andoutlet line 34 are connected to the amalgam sample source or"reservoir", such as process stream 102 which is being automaticallymonitored by monitor 10. Solenoid valve 36 normally connects line 32 to34 but is automatically activated in response to an activating signalfrom programmer 26 to connect inlet line 32 to chamber 30. Solenoid 38is normally closed but is automatically activated in response to anactivating signal from programmer 26 to connect chamber 30 to reactor14. Chamber 30 preferably has an overflow 42 which is connected tooutlet line 34 through a return flow line 41. Stream 102 wouldpreferably have differential pressure between its point of connectionwith line 32 and its point of connection with line 34 so as to forceamalgam through lines 32 and 34. An orifice 103 can accomplish this.Line 41 preferably has a vent 43 for use in connection with the cleaningof the feed tube 44, capillary tube 47 and sample chamber 30. Overflow42 allows any excess amalgam entering sample chamber 30 to flow back tothe amalgam process stream 102 via line 34 after sample chamber 30 isfilled to the predetermined volume set by the level of overflow 42.

Reactor 14 serves as a flow-through, reactor-scrubber and comprises afeed tube 44 and a reaction chamber 46. Reaction chamber 46 is a hollowglass column with two inlets 48, 50 at its lower end for connection towater supplier 16 and acid supplier 18, respectively, an outlet 52 atits upper end for connection to separator 22 and a drain outlet 53 whichis connected to a vented vessel 55 from which mercury could betransferred to some desired location for use. Feed tube 44 acts as athird inlet to reaction chamber 46 and automatically feeds the fixedvolume sample from sample chamber 30 into reaction chamber 46 upon theautomatic opening of solenoid 38. Feed tube 44 preferably includes ametering means such as a capillary portion 45 with a short length ofcapillary tubing 47 which meters amalgam from sample chamber 30 intoreactor chamber 46 at a slow enough rate to allow all the sodium to beremoved by reaction with the acid solution formed from the ingredientsfrom inlets 48 and 50. This tubing 47 is best located below the normalsurface level of liquid in chamber 46 so that it will be automaticallycleaned by the acid within chamber 46 during the times when valve 38 isclosed. The amalgam sample flows downwardly through reaction chamber 46to drain outlet 53, reacting with acid supplied through inlet 50 toproduce hydrogen gas which passes out of outlet 52. Feed tube 44projects into chamber 46 to some point below outlet 52 so that a sampleis not forced out of outlet 52. Reactor chamber 46 is preferably packedwith some turbulence-creating material, such as, for example, 6 mm glassspheres, or could have a mechanical agitator to aid in mixing thereactants from inlets 48, 50 with the sample from feed tube 44.

Water supplier 16 comprises a continuous flow, regulated pressure,regulated flow rate water supply system and thus comprises in sequence awater inlet line 54, a pressure regulator valve 56, a pressure gauge 58and a rotameter flow rate valve 60. Water supplier 16 serves to provideto inlet 48 the solvent for the reaction in chamber 46 between sodiumamalgam and mineral acid from acid supply 18. Water inlet line 54 can beconnected to a source of pressurized distilled water. If it is certainthat such source is at constant pressure, then regulator valve 56 couldbe omitted, although as a precaution it is preferred that valve 56 bepresent even then.

If an aqueous acid solution is provided by acid supply 18, watersupplier 16 could be eliminated. However, even then it is possible tohave water supplier 16 so that an operator has the option of switchingto a gaseous acid supply so that acid is continuously generated.

Acid supply 18 comprises a mineral acid reservoir such as a tank 62 ofcompressed HCl or SO₂ gas with associated gas pressure regulator valve64 and pressure gauges 65 and 66 connected to inlet 50 through a flowrate control valve such as rotameter valve 68 and mixer 70. Anynoninterfering acid could be used, such as sulfuric acid or even anorganic acid, although organic acids are somewhat weak. If an aqueousacid solution is used as the acid reservoir, an acid-resistant pump isadded between the acid reservoir and valve 68. Also, if an aqueous acidsolution is used, water supply 16 could be omitted if the acid solutionalready had sufficient water. Vales 64 and 68 are set so as to provide acontinuous flow of acid to inlet 50. The flow of acid from acid supply18 and water from water supply 16 is preferably continuous so that themolar concentration of acid in acid-water reactant mixture flowing frominlets 48 and 50 upward through the reaction chamber 46 to outlet 52 isalways above the level where 100 percent of the metallic sodium in theamalgam is reacted during the time the amalgam falls from feed tube 44to outlet 53. For HCl, that level was found to be 1.2 percent or 0.38molar when using a 3.7 ml amalgam sample containing 0.1 percent sodiumand a 50 ml reaction chamber. An acid concentration within the range offrom about 1 percent to about 99 percent could be used. An acidconcentration within the range of about 5 percent to about 40 percent ispreferred so that a smaller reaction chamber without mechanical stirrerscan be used. Acid-producing gas flow rates, H₂ O flow rates, the volumeof liquid acid in the reactor, the sample (Hg) size and the contact timebetween the amalgam and aqueous acid phases (which is determined by thelength of the reactor and the size of the packing) establish the minimumacid concentration requirements for any specific version of monitor 10.In terms of the stoichiometric amount, at least the stoichiometricamount and preferably an amount within the range of from about 8 toabout 200 times the stoichiometric amount of acid is supplied to reactor14. If a sulfuric acid solution is to be produced, SO₂ gas could beautomatically reacted with water and air or oxygen and the resultant H₂SO₄ solution fed to reaction chamber 46. The flow of acid-water reactantmixture into chamber 46 is thus automatic in the sense that no manualcontrol is necessary because the flow is continuous.

In order to serve as reference gas and carrier gas for detector 24, aninert carrier gas such as nitrogen gas is supplied for selectedintervals. The nitrogen gas is supplied by an inert gas supply such asgas supply 20 which comprises a compressed nitrogen gas tank 72 with aconventional regulator valve 74 and pressure gauges 75 and 76, areference flow line 78, a carrier gas flow line 80. Flow line 78connects valve 74 and detector 24 through a rotameter valve 79. Flowline 80 connects mixer 70 and valve 74. In line 80 is optionally placeda normally open two-way solenoid valve 82 and a flow rate control suchas a rotameter valve 84, so that a preset flow of inert gas is fed tomixer 70 upon the opening of solenoid valve 82.

Liquid-gas separator 22 is any conventional means for separating the gasand liquid flow from outlet 52 into its gas and liquid components into aliquid fraction which is passed through a vented drain line 86 to adrain 89 and a gas fraction which is fed through a detector inlet line88 to detector 24. Although in the FIGURE separator 22 is shown abovethe level of outlet 52, it would actually be lower than outlet 52 sothat acid would drain into separator 22 from outlet 52 by gravity. If anaqueous acid supply reservoir is used, the drain line 86 drains backinto the acid supply. A second liquid gas separator or "vapor trap" 23could also be added in line 88 to further separate gas from possibleresidual traces of liquid. A second drain line 87 leading into drainline 86 can drain this second separator through the valve provided indrain line 87 when and if it becomes necessary.

It would also be possible to combine reactor 14 with separator 22 as inFIG. 2 to produce an integral reactor-separator 14a. Reactor-separator14a has a chamber 46a, feed tube 44, acid inlet 50a, a carrier gas inlet51, an amalgam outlet 53, a vented vessel 55, acid outlet 52a, a venteddrain line 86a and a gas fraction outlet 88a. Acid inlet 50a is locatedabout four-fifths of the way up a side of chamber 46a at about thesurface level of the liquid within chamber 46a. Acid outlet 52a beginsabout one-fifth of the way up the side of chamber 46a and extendsupwardly to a height which determines the level of the liquid in chamber46a and then downwardly through a vented drain line 86a to an acidreservoir such as in FIG. 3. Feed tube 44 and capillary tube 47 havealready been described above. Gas outlet 88a communicates with chamber46a near the top thereof to receive the carrier gas and any gaseousreaction product such as hydrogen. Carrier gas inlet 48a communicateswith reaction chamber 46 just above the level of amalgam in drain outlet53 so that upward gas flow helps agitate the liquid in chamber 46.

Thermal conductivity detector 24 is similar to conventional two sensordevices and has a reference chamber 90 containing a reference sensor 91and a measurement chamber 92 containing a measuring sensor 93. However,it is preferable to have detector 24, unlike conventional detectors,have a non-corrosive, diffusion resistant, thermally stable plastic inorder to handle acidic gases and to last in a corrosive environment suchas in a chlor-alkali plant. Glass covered thermistors are the preferredsensors as they are more acid resistant than wire loops or resistors.Reference flow line 78 supplies inert gas such as nitrogen to referencechamber 90 while detector inlet line 88 supplies the gas fraction fromseparators 22 and 23. Gas is exhausted from reference chamber 90 througha reference exhaust 94 and from measurement chamber 92 through ameasurement exhaust 96. The flow rates through chambers 90 and 92 areregulated by valves 79 and 84, the flow through chamber 92 also beingincreased by the amount of any hydrogen gas generated by reactor 14. Aheater (not shown) could be added to detector 24 so that the gases beingmeasured are at the same temperature for added precision, as the coolingeffect of the gases depends on their temperature.

Programmer 26 can be any automatic means for sequencing the operation ofsolenoid valves 36, 37, 38 and 82 so as to perform the analysis. Amultiple cam timer is preferable, such as for example, a Model MC-6-6Timer, C-12, 12 rpm multicam timer by Industrial Timer. The multiple camswitch timer could thus be patterned after the multiple cam switchdisclosed in commonly owned U.S. Pat. No. 4,151,255 filed Oct. 11, 1977by I. A. Capuano and E. G. Miller, entitled "pH Monitor With AutomaticBuffer Standardization", except that fewer cams would be required. Inparticular, only four or five cams are needed although six cams arepreferred so that extra operations could be added later, if desired. Theprogrammer 26 receives signals from the reference sensor 91 andmeasurement sensor 93 which pass through detector signal lines 98 and100 to programmer 26 and from programmer 26 to recorder 28. The detectorsignals can be amplified, if desired, either in programmer 26, recorder28 or both.

Programmer 26 also includes a power switch 104 for selectivelyconnecting or disconnecting programmer 26 and recorder 28 from anexternal or internal power source. Programmer 26 can include a timer 106switch for automatically operating monitor 10 for only intermittentperiods, if desired. Programmer 26 would preferably have a fuse 108 toprevent electrical damage, a zero potentiometer to balance the detectorbridge.

Recorder 28 is a conventional disc or chart recorder for giving a visualreadout of the detector signal. The detector signal could also besupplied to a visual or sound alarm device or into some automaticprocess control device related to the amalgam source being measured.

Cleansing circuit 29 comprises solenoid valves 37a and 37b, liquid-acidsupply line 31, cleansing water supply line 33 and cleansing acid supplyline 35. If acid supply 18 is modified to supply aqueous acid solutionto valve 68, then line 33 and valve 37b could be omitted if noadditional water is needed for the cleansing procedure. Valves 37a and37b are normally closed solenoid valves which are simultaneously,automatically, intermittently activated by a signal from programmer 26so as to allow flow through lines 33 and 35 to line 31 and from line 31to line 32 immediately below valve 36. Valves 37a and 37b are preferablyactivated by programmer 26 during the time valve 38 is also beingactivated by programmer 26 so that the acid flows through chamber 30 andfeed tube 44 into chamber 46. Also, valves 37a and 37b are preferablyclosed before chamber 30 fills so that acid is not dumped into line 34.The acid supplied by line 31 thus passes through chamber 30, valve 38,feed tube 44 and capillary 47 to cleanse the sampling system and preventclogging. If acid would not be harmful to stream 102, then valve 33could stay open for longer periods so as to clean outlet 42 and line 41as well. Valves 37a and 37b could alternatively be manually controlledsince the cleansing operation is normally needed only intermittently,however, to help eliminate human error or forgetfulness, automaticallytimed solenoid valves are preferred. If a recirculated liquid-acidsolution were used instead of a constantly generated gas-water acidsolution then line 33 and valve 37b could be deleted. A system using aliquid-acid solution is seen in FIG. 3.

Monitor 10 is preferably built of chlorine, acid and caustic resistantcomponents so that it is able to withstand the process environment inwhich it is to be used. The monitor may include an auto-zeroing featureto correct for any baseline drift due to thermistor decay or othercauses so that a nitrogen carrier stream with some hydrogen chloridegas, such as would result from either no sample or no sodium in themercury, would produce a zero "baseline" reading.

The operation of monitor 10 of FIG. 1 will now be described. It issubmitted that the above description already has made such operationclear, however, the following description of the operation is providedfor further clarification. Monitor 10 can be utilized to monitor thesodium concentration in a sodium amalgam which can be supplied throughamalgam inlet line 32 from any source that is desired. However, monitor10 is particularly suited for use in monitoring the sodium concentrationin an amalgam process stream such as stream 102 of FIG. 1. Amalgam fromstream 102 is partially diverted through inlet line 32, valve 36 andoutlet line 34 in order that the amalgam can be sampled for measurementby monitor 10. Valve 36 is normally open to flow between lines 32 and 34and is selectively closeable to force amalgam to flow from inlet line 32to outlet line 34 through sample chamber 30 and overflow 42. Sincesample chamber 30 is of a fixed volume and overflow 42 must be at somelevel above the bottom of chamber 30, a fixed volume will be trapped inthat portion of sample chamber 30 below overflow 42. When a sufficienttime has passed to allow sample chamber 30 to be filled, programmer 26signals valve 36 to close by interrupting current flow to valve 36 toallow it to return to its normally closed position, and allow flow frominlet line 32 directly to outlet line 34. After valve 36 is closed,programmer 26 optionally sends an activating signal to optional valve 82to stop flow of inert gas through line 80 to chamber 46 and then sendsan activating signal to solenoid valve 38 causing valve 38 to move fromits normally closed position to an open position thereby allowing thesample trapped in sample chamber 30 to be dumped into reaction chamber46. After a sufficient time to allow sample chamber 30 to fully drain,programmer 26 interrupts the circuit to solenoid valve 38 causing it tomove back to its normally closed position and thereby blocking any flowfrom reaction chamber 46 into sample chamber 30. Water supplier 16 iscontinuously operated to supply water at a given pressure set byregulator valve 56 and a given flow rate set by flow rate valve 60 toreaction chamber 46. This water serves as the solvent for the reactionin reactor 14. Acid supply 18 is similarly continuously operated tosupply mineral acid, such as for example hydrogen chloride gas, at agiven pressure set by regulator valve 64 and a given flow rate set byvalve 68 through mixer 70 to reaction chamber 46.

Inert gas supply 20 is continuously operated to supply inert gas at agiven pressure set by regulator valve 74 and a given flow rate set byvalve 79 to the reference chamber 90 of detector 24. Gas supply 20 isalso automatically operable to supply nitrogen gas at the given pressureset by regulator valve 74 and a flow rate set by valve 84 through mixer70 to reaction chamber 46. Mixer 70 serves to mix the continuouslysupplied acid with the intermittently or continuously supplied inert gasfrom gas supply 20 and provide the mixture resulting therefrom toreaction chamber 46. This automatically programmed intermittent orcontinuous flow of inert gas serves as a carrier which both carries themineral acid to reaction chamber 46 and the hydrogen gas produced by thereaction within chamber 46 to liquid-gas separator 22 and fromliquid-gas separator 22 to measurement chamber 92 of detector 24. Thecontinuously supplied inert gas flowing to reference chamber 90 servesto provide a reference against which the thermal conductivity of themixture of inert gas and hydrogen gas flowing through measurementchamber 92 can be compared.

Once valve 38 has been closed and a sufficient time has passed to allowthe continuously supplied mineral acid to react with the sample withinreactor chamber 46, programmer 26 automatically stops sending anactivating signal to optional solenoid valve 82 to thereby reopen valve82 to cause inert gas to flow through line 80, valve 84, mixer 70 andinlet 50 to reaction chamber 46. The inert gas then flows throughreaction chamber 46 and carries any hydrogen gas formed out throughoutlet 52 to liquid-gas separator 22, as above described. The inert gasand hydrogen gas mixture continues to flow from liquid-gas separator 22through optional separator 23 and measurement chamber 92 to exhaust 96.During the time this mixture flows through measurement chamber 92, itacts to cool sensor 93, thereby lowering the resistance of sensor 93 andhence causing more current to flow through line 100 than otherwise. Thecooling effect of hydrogen gas is known to be greater than the coolingeffect of pure nitrogen gas so that nitrogen gas is preferred as theinert gas. However, any other gas which has a different thermalconductivity than hydrogen and which is not reactive with hydrogen gas,such as air and oxygen, can be used as the inert gas in place ofnitrogen.

Liquid-gas separator 22 is preferably a glass bulb fitted with a liquidleg (trap) to serve as a lower seal. In such a separator, the acid andinert "carrier" gas enter through the side of separator 22 into adown-facing tube. The acid falls to the bottom of the bulb and the gasexits at the top of the bulb. Separator 22 serves to separate out theliquid which is carried from reaction chamber 46 by the inert carriergas through outlet 52 into liquid-gas separator 22. Separator 22 thusdivides the aqueous acid, inert gas and hydrogen gas mixture into a gasfraction and a liquid fraction. The liquid fraction drains through avented drain line 86 to a drain 89 while the gas fraction passes throughline 88 to optional separator 23 and from separator 23 throughmeasurement chamber 92 to exhaust 96. Optional separator 23 is similarto separator 22 except that it has a drain line 87 which is valved sothat periodically any possible liquid accumulated in separator 23 can bedrained into vented drain line 86. Flow through drain line 87 isnormally closed since the flow from line 88 into separator 23 normallycontains little or no liquid. If drain line 87 was not closed, thehydrogen gas from reaction chamber 46 and separator 22 might escapethrough line 87 to vented drain line 86 and thus be lost from themeasurement. In order to drain any accumulated liquid in separator 23,line 87 is periodically opened to allow accumulated liquid to fall intovented drain line 86. Detector 24, as noted above, is a thermalconductivity detector. Such detectors are well known in the analyticalchemical are as being useful to check for gases or liquids havingdifferent thermal conductivity. Preferred as detector 24 is a dual glasscovered sensor thermistor-type thermal conductivity detector wired in aWheatstone Bridge electrical configuration. Gas from lines 78 and 88flow past sensors 91 and 93 at approximately the same rate. An imbalanceoccurs between the two detector elements when the hydrogen from theamalgamacid reaction flows past sensor 93 while gas from line 78 isflowing past sensor 91. This imbalance is measured as a change involtage by programmer 26 where it is amplified for external recording byrecorder 28.

Programmer 26 serves to control the sequence of operations of themonitor 10 and particularly controls solenoid valves 36, 38 and 82 sothat the sample is properly and completely obtained and supplied toreactor 14 and so that the reaction is allowed to occur within chamber46 prior to chamber 46 being flushed with inert gas from line 80.Programmer 26 can also contain amplifiers, if necessary, to convert thesignal from sensors 91 and 93 into a sufficiently strong signal tooperate recorder 28 and can also contain electrical circuitry to storethe peak height or peak area of the signal indication (e.g., voltageimbalance). Also, a conventional auto-zero adjustment means could beprovided to correct for any baseline drift of the converted signals fromsensors 91 and 93.

Recorder 28 can be any suitable recorder that will provide a visualrecord of the signals supplied to it by programmer 26 and electrodes 91and 93. Such recorders are readily available commercially and thereforethe detailed structure of recorder 28 will not be supplied here sincesuch details are not necessary to carrying out the invention in the bestmanner known.

Since the reaction within reaction chamber 46 serves to remove metallicsodium from the sodium amalgam, relatively pure mercury results. Thismercury drains through reaction chamber 46 into drain outlet 53 and outof drain outlet 53. This mercury can be returned through a return lineto the process stream 102 or can be supplied to any other desiredprocess or can even be stored. It will be understood that when thesample is dumped from sample chamber 30 into reaction chamber 46, theamalgam is not retained within reaction chamber 46, but rather isallowed to flow downwardly through chamber 46 to drain outlet 53. Thereason for this is that the reaction of the mineral acid supplied byacid supply 18 with the amalgam is sufficiently fast and the chamberlength sufficiently long that substantially all sodium content in theamalgam is removed during the relatively brief time that it takes theamalgam sample to pass through reaction chamber 46 to drain outlet 53.If desired, the drain outlet 53 could be provided with a valve in orderto retain the amalgam in reaction chamber 46 for additional time toallow the reaction to progress further. However, it has been found thatfor sodium amalgam there is apparently no need for such a valve or suchretention of the amalgam. Reaction chamber 46 can instead be packed withglass spheres or other nonreactive, turbulence-creating objects so as toforce the amalgam to flow along a tortuous path between tube 44 anddrain outlet 53 to give additional time and increase amalgam-acidcontact area to help the reaction to occur within the reaction chamber46.

A recirculating acid solution supplied through a pump to valve 68 is thebest mode currently envisioned for use in acid supply 18 and is analternative within the scope of the invention to acid supply 18 andwater supply 16. If such a recirculating acid solution was utilized,drain line 86 could lead to a reservoir in the acid supply in which suchsolution was contained in order that the solution be reused. Also, if arecirculating acid solution was utilized, water supplier 16 could beeliminated since the acid solution would already contain a predeterminedproportion of water. Based on preliminary calculations, a 4 litercontainer of 15 percent HCl should be able to perform about 7,000analyses of samples containing 0.1 percent sodium concentration beforebeing exhausted, based on a 3.7 milliliter sample volume of amalgam. Ifmonitor 10 were run continuously to provide a continuous sample toreaction chamber 46, acid supply 18 and water supply 16 would bepreferred so that acid could be continuously generated. If the samplingwere continuous, it would not be necessary to have a sample chamber 30but rather both the sample chamber 30 and valves 36, 38 and 82 could beeliminated. However, even if the sampling was continuous, it would bepreferable to retain sample chamber 30 and valves 36, 38 and 82 withproper sample bypasses (not shown) to allow continuous flow of sample toreactor 14 in order to have the option of switching to intermittentsampling, if the need arose.

The amount of acid used by monitor 10 is a variable, depending on thedesign of reactor 14. Sodium amalgam will completely react with lessacid or even just water if sufficient agitation is present, so amechanical agitator could be added to reactor 14 if desired. The glassbeads provide sufficient agitation for relatively low acid concentrationlevels and operate without additional power consumption orsusceptibility to mechanical breakdown of a mechanical agitator and arethus preferred.

Since amalgam is known for its tendency to build up and deposit on thelinings of components through which it flows, it is desirable tointermittently clean components whose operation could be hindered bysuch build-up. Automatic cleansing circuit 29 is designed to alleviatethis problem. Another manual cleansing alternate method will now bedescribed. A suction bulb applied to vent 43, after blocking fluidcommunicating between vent 43 and line 34 utilizing another valve inline 41 (not shown) downstream of vent 42 could draw acid from reactionchamber 46 into sample chamber 30 to clean deposits from chamber 30.This cleansing operation would also further clean capillary 47.

A monitor 10b, which is a simplified version of monitor 10, is shown inFIG. 3. Unless otherwise indicated, the reference numbers common toFIGS. 1 and 3 indicate identical items functioning in the same manner.Monitor 10b comprises sampler 12b, reactor 14, acid supplier 18b, inertgas supplier 20, liquid-gas separator 22, detector 24, programmer 26,recorder 28 and cleansing circuit 29b. Reactor 14 and gas supplier 20are the same as in monitor 10 (FIG. 1) except that carrier gas flowsdirectly to inlet 48 and mixer 70 is thus eliminated. Also, inlet 48bdoes not lead to a water supplier since acid supplier 18b provides theproper amount of water. Separator 22, detector 24, programmer 26 andrecorder 28 are the same for monitor 10b as for monitor 10. Referring toboth FIGS. 1 and 3, monitor 10b is simpler than monitor 10 because watersupplier 16 is not needed. Also, optional vapor trap 23, optionalcarrier gas shut-off valve 82, acid gas pressure gauges 65 and 66, acidgas valve 64 and acid gas tank 62 are eliminated. Acid reservoir 62b andcirculator 67 normally provide the acid supply through valve 37a at theflow rate set by rotameter valve 68. In order to assist sampling, anamalgam pump 32a is interposed in line 32. Line 42b is returnedseparately from line 34 in monitor 10b. Valve 37a in monitor 10bautomatically activates to block acid flow to inlet 50 and the flow ofcleansing acid through line 31 to sample chamber 30 at selectedintervals from about once per 40 minutes to about once per five hours.Since some acid from circuit 29b may remain in chamber 30 followingcleansing, the first few readings of recorder 28 after cleansing may belower than actual. Line 31 is preferably vented by connection thereof tovent 43.

While the invention has been disclosed in terms of a preferred methodand apparatus and an alternate method and apparatus, it will beunderstood that other alternates will be apparent to those skilled inthe art without departing from the scope of the invention and the claimsbelow are intended to cover any such alternates.

There will now be given in conclusion an example in more precise termsof the operation of the invention for purposes of illustration only.

EXAMPLE

A monitor was constructed according to FIG. 1. Sample chamber 30 wasdesigned to trap a 3.7 milliliter amalgam sample. At 0.1 percent Naconcentration in the amalgam, this gave 2 milliequivalents of sodium. Atleast 16 milliequivalents of hydrogen chloride gas were supplied by acidsupply 18 to the reactor chamber 46 to react with the sample as thesample was allowed to pass through the reactor chamber 46.

At set time intervals of a short as 2.5 minutes, valve 36 was opened tofill sample chamber 30 and then reclosed. Then valve 82 was closed for afew seconds while valve 38 was opened and the amalgam sample was reactedwith the acid contained within chamber 46. Upon completion of thereaction, valve 82 was reopened and any hydrogen gas produced by thereaction was swept by nitrogen passing through valve 82 and chamber 46to a liquid-gas phase separator 22, vapor-trap type separator 23 andthen thermoconductivity detector 24. The detector signal from electrodes91 and 93 was amplified and transmitted to recorder 28 and was readdirectly from a chart trace. Peak heights rather than peak areas weremeasured since the former was insensitive to changes in the nitrogenflow rate over the range 200-800 cc/min. Programmer 26 was a three-camtimer controlling valves 36, 38 and 82. The flow rates for water, HClgas and nitrogen gas were:

Water--50 cc/min.

HCl--600 cc/min. of air equivalent

N₂ --400 cc/min.

Amalgams of varying sodium concentration were checked both by themonitor 10 and by the standard laboratory method of reacting amalgamwith acid and measuring the hydrogen generated. The results, given inTable I below, agreed to within 2 percent.

                  TABLE I                                                         ______________________________________                                        NaHg Analyzer Precision                                                       No. of       Wet         Novel                                                Determinations                                                                             Std. Method Analyzer Difference                                  ______________________________________                                        1            0.0416      0.0417   -0.0001                                     2            0.0466      0.0485   0.0019                                      3            0.0450      0.0446   0.0004                                      4            0.0436      0.0440   0.0004                                      5            0.0449      0.0431   0.0018                                      6            0.0453      0.0465   -0.0012                                     7            0.0440      0.0432   0.0008                                      8            0.0466      0.0460   0.0006                                      9            0.0450      0.0440   0.0010                                      ______________________________________                                         No. of observation = 9                                                        Mean Average Deviation = 0.0009                                          

What is claimed is:
 1. A method of monitoring the sodium concentrationin a sodium-mercury amalgam process stream which comprises the stepsof:(a) automatically withdrawing a sample of said sodium-mercury amalgamfrom said stream; (b) automatically supplying said withdrawn sample inmetered amounts via a feed tube to a reaction zone in a reaction chamberhaving at least one inlet and at least one outlet; (c) automaticallysupplying an acid to said reaction zone in sufficient quantity so as tocompletely react with said sample to remove any metallic sodiumtherefrom and to generate hydrogen gas in proportion to the amount ofsodium in said sample; (d) separating the liquid and gaseous productsfrom the reaction of said acid with said sample via a liquid-gasseparator in fluid flow communication with said reaction chamber; (e)selectively supplying an inert gas to said reaction chamber to force thegaseous reaction products from the reaction zone into the liquid-gasseparator; (f) automatically generating a signal in response to theamount of hydrogen gas generated per unit amount of said sample from thegaseous products separated in the liquid-gas separator via detectormeans to indicate the amount of hydrogen; and (g) displaying said signalin units of sodium concentration in said amalgam stream.
 2. A method ofmonitoring the sodium concentration in a sodium-mercury amalgam whichcomprises the steps of:(a) automatically withdrawing a sample of saidsodium-mercury amalgam; (b) automatically supplying said withdrawnsample in metered amounts via a feed tube to a reaction zone in areaction chamber having at least one inlet and at least one outlet; (c)automatically supplying an acid to said reaction zone in sufficientquantity so as to completely react with said sample to remove anymetallic sodium therefrom and to generate hydrogen gas in proportion tothe amount of sodium in said sample; (d) separating the liquid andgaseous products from the reaction of said acid with said sample via aliquid-gas separator in fluid flow communication with said reactionchamber; (e) selectively supplying an inert gas to said reaction chamberto force the gaseous reaction products from the reaction zone into theliquid-gas separator; (f) automatically generating a signal in responseto the amount of hydrogen gas generated per unit amount of said samplefrom the gaseous products separated in the liquid-gas separator viadetector means to indicate the amount of hydrogen; and (g) displayingsaid signal in units of sodium concentration in said amalgam stream. 3.The method of claims 1 or 2 wherein said step of automaticallygenerating a signal further comprises the steps of:(a) supplying aninert gas at a given flow rate to a thermal conductivity detector; (b)supplying a mixture of said inert gas and said generated hydrogen gas ata given flow rate to said thermal conductivity detector; and (c)comparing the thermal conductivity of said inert gas and said mixture tothereby produce a signal indicative of the amount of hydrogen gasgenerated.
 4. The method of claim 3 wherein said inert gas consistsessentially of a gas selected from the group of nitrogen, air and argon.5. The method of claims 1 or 2 wherein:(a) said sample is of a fixedvolume; and (b) said step of automatically withdrawing is performedintermittently.
 6. The method of claim 5 wherein an amount of acidwithin the range of from about 8 to about 200 milliequivalents of saidacid are supplied to said reaction zone per milliequivalent of sodium insaid withdrawn sample.
 7. The method of claim 1 wherein said sample iscontinuously withdrawn from said stream and wherein said mineral acid iscontinuously supplied to said reaction zone.
 8. The method of claims 1or 2 wherein said acid is hydrochloric acid.
 9. The method of claim 1further comprising the step of recording said displayed signal in unitsof sodium concentration in said amalgam stream.
 10. The method of claims1 or 2 wherein said withdrawn sample is supplied at a metered rate tosaid reaction zone.
 11. The method of claim 10 further comprising thestep of automatically cleaning the device by which said metered rate isdetermined so as to produce more even metering.
 12. The method of claims1 or 2 wherein said acid is a mineral acid.
 13. The method of claim 1wherein said mineral acid is an aqueous sulfuric acid solution that ismade automatically by reacting SO₂ gas with H₂ O and air (N₄ O₂) as thecarrier gas.
 14. The method of claim 12 wherein said mineral acid is anaqueous hydrochloric acid solution.
 15. The method of claims 1 or 2further comprising the step of intermittently cleansing amalgam depositsfrom the means by which said withdrawn sample is supplied to saidreaction zone.
 16. The method of claim 1 wherein said step ofautomatically supplying said withdrawn sample includes the steps ofautomatically supplying a given volume of said withdrawn sample to asample zone, automatically returning to said sodium-mercury amalgam allof said withdrawn sample in excess of said given volume and supplyingsaid given volume to said reaction zone.
 17. The method of claim 16wherein said given volume is allowed to flow downwardly through saidreaction zone while said supplied acid flows upwardly through said givenvolume to react with the sodium therein to produce said hydrogen gas.18. The method of claim 17 wherein said given volume is supplied to saidreaction zone at a metered rate by a metering means.
 19. The method ofclaim 18 wherein said method further comprises intermittentlyautomatically cleansing amalgam deposits from said metering means withacid.
 20. The method of claim 19 further comprises intermittentlycleansing amalgam deposits from said sample zone with acid.
 21. Themethod of claim 20 wherein said intermittent cleansing of amalgamdeposits from said sample zone is performed automatically.